PROJECT SUMMARY Musculoskeletal injuries in the United States result in significant disability and high costs. Almost half of these injuries are to tendons and ligaments, including lacerations of the flexor tendons of the hand, tears of the Achilles tendon of the ankle, and tears of the rotator cuff of the shoulder. Despite significant advances in suture techniques and rehabilitation methods, outcomes after tendon repair remain unsatisfactory, with high rates of rupture and lost joint range of motion. Therefore, our long-term goal is to develop cell- and growth factor-based strategies to enhance tendon repair. Tendon healing progresses through well-defined stages of inflammation, proliferation, extracellular matrix (ECM) formation, and ECM remodeling. In our prior work, we noted a dramatic upregulation of inflammatory factors in the earliest stage of tendon healing and insufficient cell migration and ECM synthesis in the later stages of tendon healing. Recent stem cell and growth factor studies have demonstrated the potential for biologically augmenting tendon repair. In the current proposal, we will use non- invasive delivery systems to deliver adipose derived stromal cells (ASCs) and the growth factor CTGF to enhance tendon repair. Furthermore, we will elucidate the mechanisms by which ASCs and CTGF affect healing. A cell sheet approach will be used to deliver cells and a porous suture approach will be used to deliver growth factors to the repair site. These new approaches will be tested in a clinically relevant large animal flexor tendon model (although, the approaches will be generally applicable to any tendon surgical repair). Our central hypothesis is that cell therapy will modulate the early inflammatory response and growth factor therapy will modulate the later remodeling response to improve tendon healing. The first specific aim will test the efficacy of ASC cell sheets for enhancing the early inflammatory phase of tendon healing. Previously, we showed that ASCs can modulate tendon responses to inflammation in vitro and in vivo. Despite these observations, the mechanism behind the detrimental effects of inflammatory cytokines on tendon and the translational potential for modulating inflammation via stem cell therapy to enhance healing, have not been fully determined. The second specific aim will test the efficacy of ASC cell sheets combined with suture-based CTGF delivery for enhancing the late remodeling phase of tendon healing. In prior work, we demonstrated the potential for tendon regeneration via endogenous stem cell recruitment through the growth factor CTGF. Based on these in vitro and small animal studies, this aim seeks to enhance tendon healing through simultaneous delivery of CTGF and ASCs to the repair site. If successful, the proposed large animal studies can be directly translated to enhance the treatment of intrasynovial flexor tendon injuries in patients. Furthermore, the results will be broadly applicable to all tendon and ligament surgical repairs (e.g., tendons in the rotator cuff and intrasynovial ligaments in the knee).